Solar Attic Fans

05-03-2012, 06:33 PM

I'm looking into solar attic fans. My first question is why are all the solar attic fans such low wattage? My second question is do they make them that are gable mount so that I don't have to cut a big hole in my roof? Maybe an even better question is how much do attic fans help, if they even help at all?

Comment

I have 3 solar fans from Home Depot, mounted and sealed to the roof under 3 of the 5 "metro" metal roof vents. I have a continuous soffit with ducts between trusses.
I attached 60 watt panels to each of them. They spin fast.
My attic has radiant barrier on top of the fiberglass insulation and my attic temperature has lowered substantially.
135 degrees was common in the summer, now it doesn't exceed 105.
They have been in operation for over 14 months, I feel they will pay for themselves over time.

Comment

Up in the north country of New Hampshire an ac fan really didnt make much of difference in the gable ends vents. When I did a new roof I cut a continous slot the length of the roof and put a vented ridge cap on top of it, that made far more difference than the fan ever did.

I have 3 solar fans from Home Depot, mounted and sealed to the roof under 3 of the 5 "metro" metal roof vents. I have a continuous soffit with ducts between trusses.
I attached 60 watt panels to each of them. They spin fast.
My attic has radiant barrier on top of the fiberglass insulation and my attic temperature has lowered substantially.
135 degrees was common in the summer, now it doesn't exceed 105.
They have been in operation for over 14 months, I feel they will pay for themselves over time.

Comment

Up in the north country of New Hampshire an ac fan really didnt make much of difference in the gable ends vents. When I did a new roof I cut a continous slot the length of the roof and put a vented ridge cap on top of it, that made far more difference than the fan ever did.

I had that from 1991 until 2004, then Hurricane Francis blew sideways rain into the vent and flooded the attic. Hurricane Jean tried to as well, then in 2005 Hurricane Wilma blew the shingles off the roof flooding it again. We reroofed with metro roof products metal roof shingles with vents. Ridge caps are becoming scarce in Florida since the Hurricanes.

Comment

Hey Tony, up in NH if the conditions are right, I get snow blowing in the upwind gable end vents even though they are louvered. I have a big plastic tray that hangs below it to catch the snow so it can melt and evaporate before it gets into the insulation. With snow, the ridge vents can get covered with snow and stop air circulation up through the soffit vents causing ice daming, thus the gable end vents. I guess regional conditions always factor in.

Comment

how much they help is dependent on how the attic is ventilated now. But generally they are not worth much.

The use I have in mind is actually for a garage which has only small passive louvered gable vents. In the summer it gets really hot and makes the workshop area almost unusable.
I can put money into radiant barrier insulation on the inside of the uninsulated open truss roof, or powered gable fans, or something solar. Any thoughts on the respective merits of each? (Almost forgot: Currently there are no floor level or other vents in the walls, but I do have screened windows on the shaded side that can be opened if I remember.)

(I have seen discussions of line-powered fans that say the Home Depot type will only last a few years, but touting a $400 line-powered German model. Are there lifetime issues with the solar-powered DC motors?)

The summer outside temperature does not get much above 100 on the worst days, but the inside of the garage can easily get 20 degrees or more hotter at head level and intolerable up near the roof.